Surface acoustic wave filter device

ABSTRACT

In an elastic surface wave device according to this invention, an elastic surface wave element including a first and a second two-port surface acoustic wave filter and a one-port surface acoustic wave filter with a single inter-digital transducer is connected via bumps to electrodes formed on a housing by face down bonding techniques. The housing has an opening section for a ground terminal electrode in a part facing the one-port surface acoustic wave filter.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a Continuation Application of PCT Application No.PCT/JPO1/06307, filed Jul. 19, 2001, which was not published under PCTArticle 21(2) in English.

[0002] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2000-220984, filed Jul.21, 2000, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] This invention relates to an surface acoustic wave filter devicewhere an elastic surface element and a housing are assembledparticularly by face down bonding techniques.

[0005] 2. Description of the Related Art

[0006] As is generally known, surface acoustic wave filter devices arecompact and light and have a high performance and high reliability interms of functions, so that they have been widely used in variousfields.

[0007] Two-way transmission filters for mobile communication arerequired to present high attenuation characteristics to the frequencyblocking regions in their frequency characteristics. One two-waytransmission filter is so constructed that a plurality of inter-digitaltransducers (hereinafter, referred to as IDTS) are arranged in thedirection in which elastic surface waves propagate and mode-couplingtwo-port surface acoustic wave filters using the multiple resonance modeare connected in a multistage manner (an surface acoustic wave filterdevice).

[0008] To improve the frequency characteristic of surface acoustic wavefilter device more, a method of connecting a one-port resonator inseries with mode-coupling two-port surface acoustic wave filters can beconsidered.

[0009] In this case, the one-port resonator is used as a notch filter.When the attenuation pole of the one-port resonator is set near thehigh-pass region of the frequency pass band of the mode-couplingtwo-port surface acoustic wave filters, the entire frequencycharacteristic presents a sharp cut-off characteristic in thehigh-frequency region.

[0010] Here, the inventors of the present invention directed theirattention to the fact that the addition of a one-port resonator causes anew problem. The inventors concentrated their attention on the fact thatthe problem particularly arises in an surface acoustic wave filterdevice where component parts are assembled by face down bondingtechniques. In an surface acoustic wave filter device using face downbonding techniques, the notch characteristic of the one-port resonatorcannot be obtained in the desired frequency region as designed, with theresult that the entire frequency pass band characteristic of an surfaceacoustic wave filter device superior in quality cannot be obtained.

[0011] It is accordingly an object of the present invention to providean surface acoustic wave filter device which enables the notchcharacteristic of a one-port resonator to be obtained reliably near thehigh-pass region of the frequency pass band of a mode-coupling two-portsurface acoustic wave filter, even when component parts are assembled byface down bonding techniques.

[0012] Another object of the present invention is to provide an surfaceacoustic wave filter device which enables unnecessary stray capacitancecomponents in a one-port resonator to be reduced sufficiently andrealizes a frequency pass band characteristic excellent in flatness.

BRIEF SUMMARY OF THE INVENTION

[0013] To accomplish the foregoing objects, an embodiment of the presentinvention is configured as follows. In an surface acoustic wave filterdevice where the electrodes of an elastic surface wave element areconnected via bumps to the electrodes of a housing by face down bondingtechniques, the elastic surface wave element has a first two-portsurface acoustic wave filter, a one-port elastic surface wave resonatorfilter to which the output of the first surface acoustic wave filter issupplied, a second two-port surface acoustic wave filter to which theoutput of the one-port elastic surface wave resonator filter issupplied, elastic-surface-wave-element side signal input and outputelectrodes, and an elastic-surface-wave-element side ground electrodeeach formed on one face of a piezoelectric substrate. In addition, thehousing has signal input and output electrodes corresponding to theelastic-surface-wave-element side signal input and output electrodes andthe elastic-surface-wave-element side ground electrode, the groundelectrode having an opening section facing the one-port elastic surfacewave resonator filter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0014]FIG. 1A shows an example of an elastic surface wave element withmode-coupling two-port surface acoustic wave filters to help explain anembodiment of an surface acoustic wave filter device according to thepresent invention;

[0015]FIG. 1B shows an example of a housing to which an elastic surfacewave element is attached by face down bonding techniques;

[0016]FIG. 2A is a plan view showing a state where the elastic surfacewave element of FIG. 1A and the housing of FIG. 1B are laid one on topof the other;

[0017]FIG. 2B is a sectional view showing a state where the elasticsurface wave element of FIG. 1A and the housing of FIG. 1B are laid oneon top of the other;

[0018]FIG. 3 is a diagram to help explain a characteristic of a one-portelastic surface wave resonator filter;

[0019]FIG. 4 is a diagram to help explain the frequency characteristicof the surface acoustic wave filter device when a stray capacitance hasa great effect on the one-port elastic surface wave resonator filter;

[0020]FIG. 5 is a diagram to help explain the frequency characteristicof the surface acoustic wave filter device when the stray capacitance inthe one-port elastic surface wave resonator filter is reduced;

[0021]FIG. 6A shows another embodiment of the housing for the surfaceacoustic wave filter device according to the present invention;

[0022]FIG. 6B shows still another embodiment of the housing for thesurface acoustic wave filter device according to the present invention;

[0023]FIG. 7 shows an example of the elastic surface wave element of thesurface acoustic wave filter device according to the present invention;

[0024]FIG. 8 shows another example of the elastic surface wave elementof the surface acoustic wave filter device according to the presentinvention;

[0025]FIG. 9 shows still another example of the elastic surface waveelement of the surface acoustic wave filter device according to thepresent invention;

[0026]FIG. 10 shows still another example of the elastic surface waveelement of the surface acoustic wave filter device according to thepresent invention; and

[0027]FIG. 11 shows still another example of the elastic surface waveelement of the surface acoustic wave filter device according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, referring to the accompanying drawings, embodimentsof the present invention will be explained.

[0029] In FIG. 1A, numeral 11 indicates a piezoelectric substrate. FIG.1A is a plan view of the piezoelectric substrate 11 looking down on theside where an inter-digital transducer is formed. At the right and leftsides of the piezoelectric substrate 11, mode-coupling two-port surfaceacoustic wave filters 100, 200 are formed with a spacing between them.The mode-coupling two-port surface acoustic wave filters 100, 200 aremade of a metal thin film, such as aluminium (Al), by manufacturingtechniques, such as etching or evaporation.

[0030] The mode-coupling two-port surface acoustic wave filter 100 iscomposed of five IDTs (Inter-Digital Transducers) 11, 12, 13, 14, 15provided side by side and reflectors 16, 17 provided on both sides ofthese IDTs 11 to 15. As is generally known, an IDT is composed of a pairof comb-tooth-like electrodes crossing each other in such a manner thatthey are staggered.

[0031] The one-end-side comb-tooth-like electrodes of the IDTs 11, 13,15 are connected to ground terminals T11, T13, T15, respectively. Theother-end-side comb-toothlike electrodes of the IDTs 11, 13, 15 areconnected together and further connected to one electrode of an elasticsurface wave resonator filter 300 explained later. The one-end-sidecomb-tooth-like electrodes of the IDTs 12, 14 are connected in common toan input terminal TIN and the other-end-side comb-tooth-like electrodesare connected to ground terminals T12, T14, respectively.

[0032] Next, the mode-coupling two-port surface acoustic wave filter 200will be explained. This filter is composed of five IDTs 21, 22, 23, 24,25 provided side by side and reflectors 26, 27 provided on both sides ofthe IDTs 21 to 25. The one-end-side comb-tooth-like electrodes of theIDTs 21, 23, 25 are connected to ground terminals T21, T23, T25,respectively. The other-end-side comb-tooth-like electrodes of the IDTs21, 23, 25 are connected together and further connected to the otherelectrode of the elastic surface wave resonator filter 300 explainedlater. The one-end-side comb-tooth-like electrodes of the IDTs 22, 24are connected in common to an output terminal TOU and the other-end-sidecomb-tooth-like electrodes are connected to ground terminals T22, T24,respectively.

[0033] Next, the one-port elastic surface wave resonator filter 300 willbe explained. This filter is composed of an IDT 31 and reflector 32, 33provided on both sides of the IDT 31.

[0034] In the present invention, “port” means a pair of input and outputterminals. Here, input and output terminals are considered in terms ofan equivalent circuit and the number of input and output terminals isnot necessarily equal to the number of terminals in the actualconfiguration. For example, the terminal TIN of the filter 100 and thewire to which three strip lines are joined and which is connected to thefilter 300 make a pair and the terminals T11, T13, T15 and the terminalsT12, T14 make a pair, which constructs a 2-port filter.

[0035] In the mode-coupling two-port surface acoustic wave filters 100,200, five IDTs are arranged along the elastic surface wave propagatingpath of the piezoelectric substrate as shown in the figure. As isgenerally known, the pass band is obtained by coupling first-degree,third-degree, and fifth-degree longitudinal resonance modes.

[0036] In the elastic surface wave element 11 where the mode-couplingtwo-port surface acoustic wave filters have been formed as describedabove, the elastic surface wave resonator filter 300 has the followingfunction.

[0037] The mode-coupling two-port surface acoustic wave filters 100, 200each function as a band-pass filter, but their frequency characteristicspresent insufficient attenuation characteristics on the high-pass regionof the pass band. To overcome this drawback, a one-port elastic surfacewave resonator filter 300 functioning as a notch filter is formedbetween the two filters 100, 200 and used together with the two filters100, 200. The attenuation pole of the resonator filter 300 is set nearthe high-pass region of the frequency pass band of the mode-couplingtwo-port surface acoustic wave filter. This enables the high-frequencyregion of the entire frequency characteristic to present a sharp cut-offcharacteristic. This invention can achieve such performancesufficiently.

[0038] The reason for this is clarified in an explanation of FIG. 1B andFIGS. 2A and 2B.

[0039] In FIG. 1B, numeral 500 indicates a housing formed from, forexample, an alumina ceramic substrate. On its periphery, a frame 501 isprovided. That is, the housing 500 is formed into almost a flat platemade of insulating material. FIG. 1B is a plan view of the housing 500taken from above.

[0040] On the opposite face of the housing 500 to the elastic surfacewave element, ground terminal electrodes 503, 504, and an input terminalelectrode 506 and an output terminal electrode 507 corresponding to theinput terminal TIN and output terminal TOU, respectively, are formed.Between the ground terminal electrodes 503, 504, a gap (or an opening)505 is formed. The gap 505 is in a position where it faces the elasticsurface wave resonator filter 300. Therefore, the ground terminalelectrodes can be considered to have their portions facing the elasticsurface wave resonator filter 300 removed. Alternately, the groundterminal electrodes can be considered to have been divided into themode-coupling two-port surface acoustic wave filter 100 side and themode-coupling two-port surface acoustic wave filter 200 side.

[0041] In this embodiment, the width W1 of the gap 505 is greater thanthe width W2 of the elastic surface wave resonator filter 300 (or theopening L1 of IDT) (W1<W2).

[0042] The input terminal electrode 506 and output terminal electrode507 corresponding to the input terminal TIN and output terminal TOU,respectively, are formed.

[0043]FIG. 2A is a view, taken from above, of the elastic surface waveelement of FIG. 1A mounted on the housing 500 by face down bondingtechniques. FIG. 2B is a sectional view of FIG. 2A.

[0044] The ground terminals T11, T13, T15 are connected to the groundterminal electrode 503 via bumps and the ground terminals T21, T23, T25are connected to the ground terminal electrode 504 via bumps. The inputterminal TIN is connected to the input terminal electrode 506 via abump, and the output terminal TOU is connected to the output electrode507 via a bump. In FIG. 2B, a bump 601 between the input terminal TINand the input terminal electrode 506 and a bump 602 between the outputterminal TOU and the output terminal electrode 507 appear. Moreover,bumps 613, 612 between the terminals T13 and T12 and the electrode 503appear. In addition, bumps 623, 622 between the terminals T23 and T22and the electrode 504 appear.

[0045] Although not shown, a cap is provided on the top of the housing500 and the filter section is sealed.

[0046] In the surface acoustic wave filter device, when an input signalis supplied to the input terminal electrode 506, resonance occurs in themode-coupling two-port surface acoustic wave filter 100. The outputsignal of the surface acoustic wave filter 100 is input to the elasticsurface wave resonator filter 300. The output signal of the resonatorfilter 300 is input to the mode-coupling two-port surface acoustic wavefilter 200. The output of the mode-coupling two-port surface acousticwave filter 200 is taken out from the output terminal electrode 507.

[0047] Between the ground terminal electrodes 503, 504, a gap (or anopening) 505 is formed. The gap 505 is in a position where it faces theone-port elastic surface wave resonator filter 300. This enables a straycapacitance added to the elastic surface wave resonator filter 300 to bereduced sufficiently. As a result, the frequency characteristic of theelastic surface wave resonator filter 300 (or the characteristic of thenotch filter) is achieved sufficiently as designed. The attenuation poleof the elastic surface wave resonator filter 300 is set reliably nearthe high-pass region of the frequency pass band of the mode-couplingtwo-port surface acoustic wave filter. Consequently, the frequencycharacteristic of the entire device is flat, with a sharp cut-offcharacteristic in the high-frequency region.

[0048] In the explanation, to make it easy to understand theconfiguration, the elastic surface wave element has been simplified.Actually, however, 100 IDTs may be provided. The opening L1 of an IDT(see FIG. 1A) is in the range of 80 to 100 microns. The width W1 of thegap 505 is selected from the range of 10 to 200 microns.

[0049] Next, the result of measuring the frequency characteristics andother characteristics of the surface acoustic wave filter deviceaccording to the present invention will be explained.

[0050]FIG. 3 shows frequency characteristics of the elastic surface waveresonator filter 300. The ordinate indicates the amount of attenuationand the abscissa indicates the frequency. The characteristic curve 3Ashows a characteristic when an opening section is provided in the groundelectrode and the characteristic curve 3B shows a characteristic when noopening section is provided. It can be seen that the characteristicshown by the characteristic curve 3A changes sharply near 962.5 MHz.

[0051]FIG. 4 shows a frequency characteristic of the entire surfaceacoustic wave filter device. This is the frequency characteristic of theresonator filter (or notch filter) 300, with no opening section in theground electrode.

[0052] The ordinate at left indicates the amount of attenuation, beinggraduated in units of 10 dB and in units of 1 dB. The abscissa indicatesthe frequency. In FIG. 4, the characteristic curve 4A represents thefrequency characteristic of the entire device on a scale in units of 10dB. The characteristic curve 4B represents the frequency characteristicof the entire device on a scale in units of 1 dB.

[0053]FIG. 5 shows a frequency characteristic of the entire surfaceacoustic wave filter device. This frequency characteristic is thecharacteristic (or the characteristic of the device related to theinvention) when an opening section is made in the ground electrode.

[0054] The ordinate at left indicates the amount of attenuation, beinggraduated in units of 10 dB and in units of 1 dB. The abscissa indicatesthe frequency. In FIG. 5, the characteristic curve 5A represents thefrequency characteristic of the entire device on a scale in units of 10dB. The characteristic curve 5B represents the frequency characteristicof the entire device on a scale in units of 1 dB.

[0055] As seen from the comparison of the frequency characteristic withthat of FIG. 4, the pass band shows a flat characteristic.

[0056] This invention is not limited to the above embodiment.

[0057]FIG. 6A shows another example of the housing 500 used in ansurface acoustic wave filter device according to the present invention.In the above embodiment, the width W1 of the gap 505 is set greater thanthe width W2 of the elastic surface wave resonator filter 300 (or theopening L1 of IDT) (W1<W2). In the embodiment of FIG. 6A, however, thewidth W1 of the gap 505 is designed to be smaller than the width W2 ofthe elastic surface wave resonator filter 300 (or the opening L1 ofIDT). This configuration also produces the effect aimed at in thisinvention.

[0058]FIG. 6B shows still another example of the housing 500 used in ansurface acoustic wave filter device according to the present invention.In the above embodiments, the gap (or opening section) 505 is formedfrom the top end to the bottom end. In the embodiment of FIG. 6B, anopening section 505 a is formed by making a rectangular opening in partof the base 502. Forming such an opening section 505 a so as to face thearea of the elastic surface wave resonator filter 300 enables the straycapacitance in the filter 300 to be reduced. The relationship betweenthe width of the opening section 505 a and the width of the filter 300may be as shown in FIG. 1B or as shown in FIG. 6A. That is, the width W1may be smaller than (<W2) or larger than (>W2) the filter width W2 inthe direction perpendicular to the direction in which the elasticsurface wave from the elastic surface wave resonator filter 300propagates.

[0059] In this invention, the mode-coupling two-port surface acousticwave filters are not necessarily of the type explained in the aboveembodiments. In the embodiments, the elastic surface wave resonatorfilter 300 has been connected in series with the mode-coupling two-portsurface acoustic wave filters 100, 200. In contrast, as shown in FIGS. 7and 8, the elastic surface wave resonator filter 300 may be connected inparallel with the mode-coupling two-port surface acoustic wave filters100, 200. The mode-coupling two-port surface acoustic wave filters 100,200 may have the same frequency characteristic or differ from each otherin frequency characteristic.

[0060] First, in FIG. 7, on a piezoelectric substrate 11, twomode-coupling two-port surface acoustic wave filters 100, 200 and anelastic surface wave resonator filter 300 connected in series with themode-coupling two-port surface acoustic wave filters 100, 200 are formedfrom a metal thin film, such as aluminium (Al).

[0061] The mode-coupling two-port surface acoustic wave filter 100 iscomposed of three IDTs 1 a, 1 b, 1 c provided side by side, reflectors 1e, 1 f provided on both sides of the IDTs 1 a, 1 b, 1 c, and a terminalelectrode 1 g connected to a comb-tooth-like electrode constituting theIDT 1 b. The mode-coupling two-port surface acoustic wave filter 200 iscomposed of three IDTs 2 a, 2 b, 2 c provided side by side, reflectors 2d, 2 e provided on both sides of the IDTs 2 a, 2 b, 2 c, and a terminalelectrode 2 f connected to a comb-tooth-like electrode constituting theIDT 2 b.

[0062] The elastic surface wave resonator filter 300 is composed of anIDT 3 a and reflectors 3 b, 3 c provided on both sides of the IDT 3 a.

[0063] In FIG. 8, on a piezoelectric substrate 11, two mode-couplingtwo-port surface acoustic wave filters 100, 200 and an elastic surfacewave resonator filter 300 connected in parallel with the mode-couplingtwo-port surface acoustic wave filters 100, 200 are formed from a metalthin film, such as aluminium (Al).

[0064] The mode-coupling two-port surface acoustic wave filters 100, 200have the same configuration as shown in FIG. 7. The elastic surface waveresonator filter 300 has the same configuration as shown in FIG. 7.However, the example shown in FIG. 8 differs from that of FIG. 7 in theposition where the elastic surface wave resonator filter 300 isprovided.

[0065]FIGS. 9, 10, and 11 show still other embodiments of an surfaceacoustic wave filter element.

[0066] In FIG. 9, on a piezoelectric substrate 11, two mode-couplingtwo-port surface acoustic wave filters 100, 200 and an elastic surfacewave resonator filter 300 connected in series with the mode-couplingtwo-port surface acoustic wave filters 100, 200 are formed from a metalthin film, such as aluminium (Al).

[0067] The mode-coupling two-port surface acoustic wave filter 100 iscomposed of five IDTs provided side by side, reflectors provided on bothsides of the IDTs, and a terminal electrode 1 f serving as a signalinput section. The mode-coupling two-port surface acoustic wave filter200 is composed of five IDTs provided side by side, reflectors providedon both sides of the IDTs, and a terminal electrode. The elastic surfacewave resonator filter 300 is composed of an IDT, reflectors provided onboth sides of the IDT, and a terminal electrode 2 f serving as a signaloutput section.

[0068] In FIG. 10, on a piezoelectric substrate 11, two mode-couplingtwo-port surface acoustic wave filters 100, 200 and an elastic surfacewave resonator filter 300 connected in series with the mode-couplingtwo-port surface acoustic wave filters 100, 200 are formed from a metalthin film, such as aluminium (Al).

[0069] The mode-coupling two-port surface acoustic wave filter 100 iscomposed of seven IDTs provided side by side, reflectors provided onboth sides of the IDTs, and a terminal electrode 1 f serving as a signalinput section. The mode-coupling two-port surface acoustic wave filter200 is composed of seven IDTs provided side by side, reflectors providedon both sides of the IDTs, and a terminal electrode 2 f serving as asignal output terminal. The elastic surface wave resonator filter 300 iscomposed of an IDT and reflectors provided on both sides of the IDT.

[0070] In FIG. 11, on a piezoelectric substrate 11, two mode-couplingtwo-port surface acoustic wave filters 100, 200 and an elastic surfacewave resonator filter 300 connected in series with the mode-couplingtwo-port surface acoustic wave filters 100, 200 are formed from a metalthin film, such as aluminium (Al).

[0071] The mode-coupling two-port surface acoustic wave filter 100 iscomposed of three IDTs provided side by side, reflectors provided onboth sides of the IDTs, and a terminal electrode 1 f serving as a signalinput section. The mode-coupling two-port surface acoustic wave filter200 is composed of seven IDTs provided side by side, reflectors providedon both sides of the IDTs, and a terminal electrode 2 f serving as asignal output terminal. The elastic surface wave resonator filter 300 iscomposed of an IDT and reflectors provided on both sides of the IDT.

[0072] To incorporate an elastic surface wave element as shown in FIGS.7 to 11 into the aforementioned housing 500, the ground terminalelectrode corresponding to the elastic surface wave resonator filter hasonly to be removed.

[0073] This invention is not limited to the above-described embodimentsand may be practiced or embodied in still other ways without departingfrom the sprit of essential character thereof.

[0074] As has been explained in detail, with the present invention, itis possible to provide a very good surface acoustic wave filter devicewhich is capable of reducing the unnecessary stray capacitance componentsufficiently even with a configuration formed by face down bondingtechniques and which is also capable of realizing a practical pass bandcharacteristic excellent in flatness.

[0075] An surface acoustic wave filter device according to thisinvention can be used in the field of electronic apparatuses, includingmobile communications equipment and television sets.

What is claimed is:
 1. An surface acoustic wave filter device where theelectrodes of an elastic surface wave element are connected via bumps tothe electrodes of a housing by face down bonding techniques, the surfaceacoustic wave filter device being wherein the elastic surface waveelement has a first two-port surface acoustic wave filter, a one-portelastic surface wave resonator filter to which the output of the firstsurface acoustic wave filter is supplied, a second two-port surfaceacoustic wave filter to which the output of the one-port elastic surfacewave resonator filter is supplied, elastic-surface-wave-element sidesignal input and output electrodes, and an elastic-surface-wave-elementside ground electrode each formed on one face of a piezoelectricsubstrate, and the housing has signal input and output electrodescorresponding to the elastic-surface-wave-element side signal input andoutput electrodes and the elastic-surface-wave-element side groundelectrode, the ground electrode having an opening section facing theone-port elastic surface wave resonator filter.
 2. An surface acousticwave filter device according to claim 1, wherein the opening section isso configured that the part facing the first two-port surface acousticwave filter and the part facing second two-port surface acoustic wavefilter are separated electrically from each other.
 3. An surfaceacoustic wave filter device according to claim 1, wherein the openingsection is formed into a rectangular shape.
 4. An surface acoustic wavefilter device according to claim 1, wherein the first one-port surfaceacoustic wave filter is connected in series with the first and secondtwo-port surface acoustic wave filters.
 5. An surface acoustic wavefilter device according to claim 1, wherein the one-port surfaceacoustic wave filter is connected in parallel with the first and secondtwo-port surface acoustic wave filters.
 6. An surface acoustic wavefilter device according to claim 1, wherein the first and secondtwo-port surface acoustic wave filters have the same frequencycharacteristic.
 7. An surface acoustic wave filter device according toclaim 1, wherein the first and second two-port surface acoustic wavefilters differ from each other in frequency characteristic.
 8. Ansurface acoustic wave filter device according to claim 1, wherein thefirst and second two-port surface acoustic wave filters have the samenumber of inter-digital transducers.
 9. An surface acoustic wave filterdevice according to claim 1, wherein the first and second two-portsurface acoustic wave filters differ from each other in the number ofinter digital transducers.